The Newfoundland Breeding Colony has been developed as a source of laboratory dogs affected with left ventricular hypertrophy (LVH) due to infracoronary left ventricle outflow tract obstruction and other spontaneously occurring heart defects. More than 100 dogs have been reared, all having some form of hereditary subaortic stenosis (SAS), with one family demonstrating pulmonic valve stenosis and SAS. Numbers of animals have been used for regional myocardial blood flow studies of the hypertrophied ventricle and evaluation of corrective surgery techniques using apico-aorta prosthetic devices.